1. Field of the Invention
The present invention relates to an internal combustion-operated setting tool for driving fastener elements such as nails, bolts, pins into a substrate, having a fuel source, with a fuel feed line from a fuel source to a combustion chamber and having at least one dosing device, which is arranged between the fuel source and the combustion chamber. A displacement body is arranged in a chamber in the dosing device for forcing fuel out of the chamber. This type of setting tool can be operated using gaseous or liquid fuels, that are burnt in a combustion chamber and wherein a drive piston for fastening elements is driven.
2. Description of the Prior Art
Generally, there is the problem of dosing the fuel for each work cycle with a calibrated quantity of a corresponding air or oxygen mix as the oxidation agent. The oxygen quantity available for the combustion process is heavily dependent on the ambient temperature as well as on the air pressure and humidity. The required fuel quantity therefore varies with the aforementioned parameters quite substantially—in the extreme case up to 40%. These variations can have adverse ramifications on the combustion of the air-fuel mixture if the air-fuel mixture is too rich or too lean in fuel. It is therefore desirable to match the fuel quantity to the respective ambient conditions.
An internal combustion-operated setting tool of this general type is described in EP 0 597 241, wherein the metered feed of the fuel from the fuel source to the combustion chamber is done via a dosing device, which comprises a valve actuated by a solenoid, which is normally closed. The actuation is effected electronically by a switch circuit, which reacts to a switch and opens the valve for a controllable set time interval to enable a flow of the fuel from the fuel source to the combustion chamber.
The drawback is that with varying upstream pressure in the fuel source, the flow rate of the fuel is variable and accordingly results in imprecise dose quantities.
DE 42 43 617 A1 further discloses a setting tool, wherein a gas inlet valve is mechanically opened, in a work cycle, such that fuel from a fuel source reaches a holding space, which communicates with the environmental air. A pressure or eventually a temperature equalization with the environmental air can take place via this connection, such that an adapted air-fuel mixture reaches the combustion chamber. From this holding space the fuel then reaches the combustion chamber at the appropriate time. The disadvantage is that a fuel loss can occur via the communication to the environmental air. In addition, the pressure in the dosing chamber cannot be regulated.